1. Field of the Invention
The present invention relates to a magnetic head for recording and/or reading back information in an apparatus using a magnetic recording medium which holds information according to magnetic changes in a magnetic recording film formed over the surface of the medium, and more particularly, the invention relates to the structure of a magnetoresistive thin film magnetic head capable of high-sensitivity and high-resolution recording and reading back, and a production method therefor.
2. Description of the Background
In recent years, there has been rapid progress made-in high-density recording technology for use in magnetic disk apparatuses resulting in a successful capacity enlargement and size reduction of such apparatuses. The core of such high-density recording technology is a magnetoresistive thin film magnetic head (“MR head”) with a high read-back output. Ongoing efforts to improve the structure of magnetoresistive elements (“MR elements”) with a view toward achieving ever higher outputs continue. The focus of these attempts is a structure known as a spin valve type.
An MR head is mounted with an MR element manifesting a magnetoresistive effect as a magnetic head dedicated to read-back use. The basic structure of an MR head is shown, for example, in FIG. 5 of JP-A-114119/1993. An MR element typically includes outlet terminals made of a non-magnetic conductive metal joined to the MR element in a “sandwich-style” orientation. These outlet terminals let a sense current flow and detect variations in the resistance of the MR element due to leakage fluxes from the medium as a variation in voltage.
On both sides of the MR element, there are provided magnetic shields made of a soft magnetic substance such as NiFe via a non-magnetic insulating layer of Al2O3 (or similar materials) arranged substantially in parallel to the MR element. This shielding structure can restrict the magnetic fluxes leaking into the MR element from the medium to those coming in through the air bearing surface of the MR element which thereby enhances the resolution of read-back.
Attempts have also been made to increase the sensitivity and minimize the size of MR elements to meet the need for ever greater density in recording and reading back applications. Where an MR element of such a fine structure is to be used, if its tip is directly exposed on the air bearing surface (head flying surface), the outlet terminals may become short-circuited during the grinding process undertaken to expose the MR element or by dust accumulating on the medium. If the outlet terminals are short-circuited in this way, the rate of resistance change of the MR element will drop heavily or the read-back noise may increase, both of which may result in a significant deterioration in the quality of the read-back signals.
For example, a tunneling magnetoresistance (TMR) element, currently known in the art as a highly sensitive MR element, is only about 20 nm in overall thickness, and its insulating layer, separating the free layer and the pinned layer within the magnetic body from each other, is no more than approximately 1 nm thick. The short-circuiting problem is particularly acute with this TMR element. Therefore, it is preferable to form the MR element away from the air bearing surface and to provide a flux guide for guiding leakage fluxes from the medium toward the MR element instead. This circumstance is described in, for example, Nikkei Electronics, No. 774 (Jul. 17, 2000), p. 182.
A disadvantage in utilizing the flux guide structure lies in the insufficient magnetic resistance between the flux guide and magnetic shields sandwiching it. This insufficiency invites absorption by the magnetic shields of the magnetic fluxes flowing into the flux guide. As a result, magnetic fluxes from the magnetic recording medium decrease before they reach the MR element, and only part of the magnetic flux quantity flowing from the medium into the flux guide contributes to the read-back output.
Methods for improving this flux guide structure limitation are specifically described in, for example, JP-A-114119/1993 cited above and JP-A-150258/1994. In an MR head described in either of these documents, the shape of magnetic shields is improved which preferably results in an enhanced magnetic flux induction efficiency of the flux guide. Thus, it is a structure in which the spacing between the magnetic shields is narrowed near the air bearing surface of the head to restrict magnetic fluxes flowing into the flux guide, while the magnetic shields are arranged away from the flux guide inside the head to reduce the flow of magnetic fluxes from the flux guide to the magnetic shields.
The structure disclosed in either of the above-cited patent applications makes it possible to keep the magnetic resistance between the flux guide and the magnetic substance of the magnetic shields greater than that between magnetic shields arranged in a planar form. Accordingly, the read-back sensitivity of the MR head having this flux guide structure is enhanced.
However, even in these improved structures according to the prior art, the magnetic shields are formed in a direction substantially parallel to the flux guide, i.e. a direction perpendicular to the air bearing surface, except that there is some level gap. Therefore, even these structures cannot prevent magnetic fluxes from flowing out of the flux guide, and this outflow of magnetic fluxes may be even more pronounced where the flux guide is extended in length.
In order to achieve an improved level of magnetic flux induction efficiency, it is necessary to increase the level gap between magnetic shields and to secure a wide angle in the level gap part. It is also essential to accurately control the distance between the level gap and the air bearing surface.
An exemplary process for forming magnetic shields with a level gap like those in the above-described conventional structures will now be described with reference to FIG. 1. Initially, a magnetic head base 11 is prepared as shown in FIG. 1A. A flux guide, a magnetic flux detecting element consisting of a magnetoresistive effect, electrodes accompanying the magnetic flux detecting element and an insulating layer are preferably built into this magnetic head base 11 in advance. Thereafter, a level gap of resist 12 is formed by photolithography (FIG. 1B). After the angle of the level gap part is appropriately adjusted by high-temperature baking or another process (FIG. 1C), a soft magnetic material, such as NiFe, is formed into films 13 to prepare shields by plating (FIG. 1D). Finally the slider bottom is ground to determine the air bearing surface 14 (FIG. 1E). This production process is conventionally used as a method to form a level gap in the upper magnetic pole or the like of a recording head and is illustrated in, for example, FIG. 10 of JP-A-258236/1993.
However, utilizing the production process described above to fabricate exemplary devices has revealed potential problems. For example, where a large level gap is formed in a sharp angle in this process, it is difficult to control the way in which a plating film is stuck to the level gap part, and the formation of shield films in the level gap part is susceptible to frequent fault. For instance, FIG. 1D′ illustrates the result of plating from the step of FIG. 1B with the step of FIG. 1C dispensed with. As is understood from the state of the level gap shown in FIG. 1D′, plated magnetic shields are partly thinned, resulting in an inadequate shielding effect in this part.
At the step of easing the angle of the level gap part shown in FIG. 1C, the starting position of the level gap (the ending position of the resist) substantially fluctuates from head to head. Consequently, in the grinding process shown in FIG. 1E, the closer the starting position of the level gap is to the air bearing surface, the greater the deviation of the distance from the air bearing surface of the magnetic head to the starting position of the level gap, which may result in a more pronounced fluctuation of read-back sensitivity. Enhancing the efficiency of magnetic shields without deviating from conventional structures has its own inevitable limit imposed by the production process.